Monitoring and regulating the tension in a material is necessary in innumerable arts. For example, in the tire industry, it is important that heated uncured or "green" rubber be given a chance to relax and not exceed a preselected tension before it is cut into lengths which form tire components, or else when assembled these cut pieces will not be of the correct length. Relaxation is accomplished by transporting a strip of uncured rubber down a plurality of cooling conveyors arranged in series at progressively lower heights. As the rubber strip "steps" from one conveyor to the next, the various conveyor speeds are adjusted to maintain a shallow loop in the strip providing near zero tension therein and facilitating such relaxation.
In order to insure that such relaxation is continuously maximized, transducers have been provided to monitor the position of the rubber strip (and thereby monitor the profile of the loop) as it is transported from one conveyor to the next. Typically these transducers were simply either a conventional potentiometer, a control transformer with a rotatable secondary, or an A.C. reactor with a movable iron core. Since these transducers are interconnected with conveyor speed control circuitry requiring D.C. operation, the latter two devices, which had to be operated in an A.C. environment, required special circuitry for conversion to and compatibility with a D.C. system.
In other arts transducers for monitoring and regulating the position of a material have employed dancer rollers acting through various linkage mechanisms to control light passing from a lamp to a light sensitive element that generates a discrete electrical signal when the light was incident thereupon. For example, in U.S. Pat. No. 3,092,764 a photoelectric tension sensing motor control circuit is disclosed as having a notched light filter disc fixed to a dancer roller to discretely control light from a single light source to two photocells based upon the tension of a web or strand collecting on a take-up roll. However, conveyor speed control circuitry ideally operates with a single, analog, bipolar D.C. signal which conveys not only information regarding position of the dancer roller, but its direction from a preselected reference axis, something a device as that disclosed in U.S. Pat. No. 3,092,764 is incapable of furnishing.